Cannabis Seedling Problems and How to Fix Them

The early stages of life for any life form are absolutely crucial for normal, healthy development down the road and cannabis plants are no exception.  Yes, cannabis is a hearty, robust plant that can withstand a lot of abuse, but to give it some of that vigor, it needs a solid foundation, in other words, a healthy seedling stage that will allow it to develop into the best possible plant. The very first thing to keep in mind when you’re trying to generate a healthy seedling is the starting material, you want high-quality seeds with a good germination rate. This is up to the breeder or seedbank you are sourcing your seeds from, so remember to choose wisely!

Cannabis Seeding Stage

The seedling stage is when plants are most delicate and vulnerable, so particular attention and care are required. In nature, not all cannabis seedlings make it to the next stage, however if looked after properly, a grower can easily take some precautions to make sure his or her seedlings end up developing big, beautiful and healthy buds. Before we get into how to properly care for a seedling, let’s define one first.

Once the seed has sprouted and shed its husk, it will typically display a set of two, small leaves with smooth, rounded edges known as cotyledons. Soon after, the first set of tiny serrated leaves, also known as true leaves, will appear, indicating your seedling is healthy and ready to develop some more nodes from the center of the stem. Over the coming days, more serrated leaf sets will appear until the plant takes on a more recognizable shape. The whole seedling stage typically lasts for about 2-3 weeks, but what takes place in this period is crucial for the end result.

What Should a Healthy Cannabis Seedling Look Like?

Size

In the early stages, a healthy cannabis seedling is generally small, growing to about 2 to 4 inches in height by the end of the seedling stage.

Leaves

Initially, the seedling will develop a set of round leaves called cotyledons. After this serrated leaves will begin to grow. A healthy cannabis seedling should have vibrant green leaves. The color is an indicator of proper nutrient absorption.

Stem

A healthy stem is vital for supporting the plant. It will be thin at first but should be able to stand upright. The stem transports nutrients and water throughout the plant. A sturdy stem indicates good cell structure and overall health.

Most common seedling issues and how to deal with them

Prevention is the best medicine, however mistakes can still be made, particularly if you are new to the game. Thankfully, even if you do make a mistake, you generally still have enough time to fix it and get things back on track.

Overwatering

Overwatering is perhaps one of the most common problems growers encounter and not just in the seedling stage. The problem with overwatering is not so much the excess water but rather the lack of oxygen, which will make plants droop and appear sickly. If left untreated, they will start to turn yellow and ultimately die. Sure, people grow plants hydroponically all the time, but even then, oxygen is dissolved in the water, making sure that plant roots get the O₂ they need to survive. If you are growing in a solid medium, the best way to avoid the effects of overwatering and/or poor drainage are as follows:

• Remove any excess runoff water so that roots can breathe
• Use containers such as air pots or those made out of breathable material, avoid plastic ones
• Improve your soil drainage by mixing in vermiculite, perlite, pebbles, sand, etc.
• If using plastic containers, make drainage holes
• Don’t water too frequently, only when the top layer of the soil feels dry
• Use smaller amounts of water

Underwatering

Another common cannabis seeding problem, this usually happens when growers try to overcompensate after being told not to overwater their plants. If simply underwatered, seedlings will turn yellow, wilt and die, similar to overwatering. However, if you are underwatering AND feeding them too many nutrients, they will tend to turn a darker shade of green, twist their leaves and the plant’s growth may be stunted. To prevent this from happening:

• Keep the top layer of the soil moist
• Make sure the soil has good water retention by including vermiculite/perlite in the mix or some other water-retaining amendment such as coco coir

Nutrient toxicity/deficiencies

Many novice growers are all too excited to be the best grower possible and needlessly overfeed their seedlings with too many nutrients, giving them a “hot soil” that will lead to “nute burn” or nutrient toxicity. When seedlings have too many nutrients, they will turn yellow, develop spots, become brittle (crispy) or show some other type of discoloration. Yellow or bright leaf tips are a typical indicator that your soil is too hot, leading to toxicity. Another common problem for seedlings is a pH imbalance. Your seedlings’ soil should have a pH between 6.0 and 7.0 (ideally around 6.5) for soil and 5.5-6.2 for hydroponic setups in order to avoid nutrient lockout. To avoid nutrient deficiencies/excess:

• Feed your seedlings only water for the first week or two as they don’t need that many nutrients at this stage, the medium should have enough for them to survive on
• Check and adjust the pH accordingly, this is the cause and solution to many nutrient issues early on

Temperature issues

The bulk of temperature problems for seedlings will result from excess heat as　seedlings can survive at lower temps, though growth will be slowed. When things get too hot, your plants will display dry/crackly leaves that are yellowish/greenish in color, sometimes leaves may develop taco/canoe-like shapes. Another indicator that the temperature is too high is cracks in your grow medium/soil. To avoid overheating your seedlings:

• Place them at the right distance from your light source. If you’re not sure of the distance between your seedlings and your lighting fixture, put your hand directly under your lamp. If you feel the burn in your hand, your seedlings most definitely will as well.
• Keep an eye on the temperature, the ideal range for cannabis seedlings is 68-77° (20-25°C) and make sure the humidity is appropriate as seedlings like things to be moist (65-70% relative humidity).
• Use a lighting fixture that doesn’t generate excess heat, such as fluorescent lamps or LEDs. HID lamps usually generate a lot of heat and aren’t recommended for seedlings.

Light issues

Light is absolutely crucial for all plants to survive as photosynthesis is their main food source. Insufficient or excess light is also a common issue that growers face, though if neglected, that could mean the end of your seedlings. Seedlings that don’t get enough light will stretch towards the light source and develop excessive internodal spacing, which means they can easily fall over. Seedlings getting too much light will tend to have burnt, crispy leaves. The good news is that in both cases the issue is usually an easy fix.

• Adjust the height of your lighting fixture to find the ideal temperature, you may need to do this frequently over the course of the seedling stage.
• Use a light source that doesn’t generate too much intense light, such as compact fluorescent lights or LEDs.

Humidity Levels

Ideal humidity for cannabis seedlings is between 60-70%. Maintaining this range ensures proper growth and water absorption through the leaves.

• For high humidity: Increase ventilation, use a dehumidifier, or place a fan to circulate air.
• For low humidity: Use a humidifier, place a tray of water near the plants, or use a wet cloth hanging in the grow space.

Seedlings With a Seed Shell Stuck to Them

Sometimes the seed’s outer shell may stick to the cannabis seedling’s leaves. This usually happens if the seed wasn’t properly cracked open during germination. To fix this, you can gently remove the shell using tweezers. Be extremely careful to not damage the seedling.

Key Tips on Growing a Cannabis During the Seedling Stage

Ideal Seedling Environment

Creating the ideal environment is crucial. This includes maintaining humidity levels between 60-70%, temperature around 22-26°C, providing adequate lighting, and ensuring the soil has naturally occurring nutrients.

Overly Wet Soil

Seedlings are prone to damping off in overly wet soil. It’s essential to avoid overwatering. Use a well-draining soil and ensure that your pots have drainage holes.

Soil Too Dry

Seedlings need moisture. If the soil is too dry, it can stunt their growth. Make sure to water them lightly but consistently to keep the soil slightly damp.

Proper Watering

Overwatering or underwatering cannabis seedlings can be detrimental. It’s important to keep the soil consistently moist but not soggy. Water lightly and monitor the soil conditions.

Planting Too Deep

Plant seeds at a depth of 1-3cm. Avoid packing the soil too tightly as this can inhibit growth. Planting too deep or compacting the soil can prevent the seedling from breaking through the surface and growing.

Ideal Temperature

Maintain a temperature range of 22-26°C for cannabis seedlings. This range is ideal for promoting healthy growth without stressing the plant.

Cannabis Seedling FAQ

How long does a cannabis plant stay in the seedling stage?

Cannabis seedlings 2-3 weeks or until they product their first set of true leaves. True leaves are the serrated edged leaves and normally show after 3-4 sets of cotilydons.

Should you mist cannabis seedlings?

Yes, lightly, to maintain humidity. However, avoid misting too heavily when the light is directly on the plant. ideally you should mist the surface of the soil.

How much light do cannabis seedlings need?

14-18 hours per day. 18 hours of light and 6 hours of darkness is commonly recommended.

How close should the light be to seedlings?

15-30 inches, depending on the light source.

Is windowsill light enough for cannabis seedlings?

It can be, but usually, supplemental light is needed for optimal growth. It really depends on how much light the window gets.

In Conclusion

The seedling stage lasts only a couple of weeks, but what you do to them in this period will have a major impact on the final product. Ideally, your seedlings should be in a warm, humid environment with a good amount of light and not too many nutrients. Keeping things simple is the best way forward here and your plants will reward you with a bountiful harvest down the road. Happy growing!